Instrument panel reinforcement structure including a novel driver side cross tube

ABSTRACT

A light weight, structurally stiff instrument panel reinforcement structure for motor vehicle bodies. The reinforcement structure includes driver side and passenger side cross tubes that are preferably aluminum alloy extrusions, and a center stack support that is preferably a magnesium alloy casting connecting the cross tubes. The driver side cross tube supports a steering column assembly. The driver side cross tube has a greater average wall thickness than the passenger side cross tube. The driver side cross tube is hydroformed so that a middle portion has larger bending and torsion resistance than the end portions.

PENDING RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 08/995,29 1,filed Dec. 19, 1997 for “Light Weight Instrument Panel ReinforcementStructure”.

FIELD OF THE INVENTION

The present invention relates to an instrument panel reinforcementstructure for motor vehicles. The reinforcement structure extendsbetween two front pillars and supports a steering column, a glove box, apassenger side air bag and various other instrument panel components.

BACKGROUND OF THE INVENTION

The instrument panel reinforcement structure is the part of a motorvehicle extending between left and right front pillars in front of thepassenger compartment. Various components mounted on the instrumentpanel reinforcement structure include the steering column assembly, aglove box, a passenger side air bag, an instrument cluster, anentertainment/information system, a heating/ventilation/air conditioningunit with associated ducts, a wire harness, electrical modules andfascia. The inclusion of driver side air bags and the locating of somecontrols in the steering column assembly have caused it to gain weightand to grow in size.

Passenger vehicles have been made safer in recent years through the useof safety devices such as seat belts and air bags. In addition,automobile manufacturers are making the body and its associatedcomponents more energy absorbent in the event of a collision. The UnitedStates government has also established a set of Motor Vehicle SafetyStandards mandating certain other minimum vehicle safety requirements.

In the prior art, some attempts have been made to provide instrumentpanel structural reinforcement assemblies for motor vehicles. However,the prior art assemblies generally suffer from one or more seriousdisadvantages making them less than entirely suitable for their intendedpurpose. For example, steel assemblies have been used for some time butthey add considerable weight to vehicle bodies. Accordingly, there is aneed for an alternative to steel instrument panel assemblies.

Onitsuka U.S. Pat. No. 4,560,186 describes an automobile instrumentpanel assembly supported by a reinforcement 4 comprising a pipe 5extending between two pillars 3. The pipe has a uniform size in thecross-car direction. A steering column mounting bracket made up of metalsheets is welded to the pipe 5 on the right (driver's) side. Onitsuka'sassembly is difficult to manufacture economically because it includes somany individual parts welded to the pipe 5. Accordingly, there stillremains a need for a stiff, light weight, economically manufacturableinstrument panel reinforcement structure.

A principal objective of our invention is to provide a light weightinstrument panel reinforcement structure for motor vehicles that hasenhanced structural stiffness in order to minimize steering columnvibrations.

A related objective of the present invention is to provide an instrumentpanel reinforcement structure for motor vehicles made from aluminumalloy and magnesium alloy components. The reinforcement structure of thepresent invention offers about a 40% weight saving compared with similarsystems having steel components. The preferred reinforcement structureshown and described herein weighs only about 18 pounds (7.7 kg).

Another objective of the invention is to provide a light weightinstrument panel reinforcement structure that consumes little additionalcockpit space and is inexpensive to manufacture and to install on a massproduction assembly line.

A further objective of our invention is to provide an instrument panelreinforcement structure that adapts easily to left and right hand drivecars and accommodates different steering column orientations.

One important advantage of our invention is that it has a common basestructure adaptable to a variety of different designs by addition orswapping of components, thereby reducing effort, time and cost requiredfor engineering the instrument panel structural system.

Additional objectives and advantages of our invention will becomeapparent to persons skilled in the art from the following detaileddescription.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a lightweight instrument panel reinforcement structure for inclusion in a motorvehicle body having a floor panel and several pillars extending upwardlyfrom the floor panel. The reinforcement structure extends between theleft and right front pillars in front of the passenger compartment. Thereinforcement structure supports a steering column, a glove box, apassenger side air bag and various other instrument panel components.

A preferred instrument panel reinforcement structure comprises apassenger side cross tube and a driver side cross tube connected by acenter stack support. The cross tubes are preferably connected to thefront pillars through metal brackets. The center stack support ispreferably connected to the floor panel. Mounting tubes attached to thedriver side cross tube support the steering column. The passenger sideair bag support is attached to the passenger side cross tube. A driverside knee bolster is connected to the driver side cross tube throughmetal crush tubes. Metal crush tubes also connect a glove box door frameto the passenger side cross tube.

The driver side cross tube and the passenger side cross tube arepreferably aluminum alloy extrusions. Aluminum alloys of the AluminumAssociation (AA) 6000 series are preferred although other alloys mayalso be used. The AA 6000 alloys including AA5000 series alloysgenerally contain about 0.2-2 wt. % silicon and about 0.2-2 wt. %magnesium. These aluminum alloys usually also contain other alloyingelements and some impurities. Our particularly preferred cross tubes aremade with an AA 6063 T4 alloy containing about 0.2-0.6 wt. % Si,0.45-0.9 wt. % Mg, 0.35 wt. % max. Fe, 0.10 wt. % max. Cu, Cr, Zn andTi, remainder Al, incidental elements and impurities.

A particularly preferred driver side cross tube is extruded as a hollowoval having a 120×60 mm cross-section with an average 5 mm wallthickness. The extruded cross tube is hydroformed in a middle portion toprovide a generally triangular cross section with a flat bottom surfaceappropriately oriented for attachment of two steeling column supporttubes. The cross tube also includes two openings for crush tubescontacting a driver side knee bolster. The steering column support tubesare preferably AA 6063-T4 aluminum alloy extrusions having a wallthickness of about 5 mm. A particularly preferred passenger side crosstube is a hollow cylinder having an outer diameter of about 60 mm and awall thickness of about 3 mm. The driver side cross tube and thepassenger side cross tube both extend laterally or in a cross-cardirection, on opposite sides of a center stack support. An importantfeature of our invention is that the driver side cross tube has greateraverage wall thickness than the driver side cross tube. outwardly of thecenter stack support and a first wall having a thickness that isgenerally constant across the first length. The driver side cross tubehas a second length extending laterally outwardly of the center stacksupport and a second wall having a thickness t₂ that is generallyconstant across the second length.

The driver side cross tube is preferably reformed by a process thatincludes pressurizing the tube internally with an incompressible fluidat sufficient pressure to deform the middle portion inside a die. Theincompressible fluid is preferably water at a pressure of about100-5,000 psi, more preferably about 1,000-3,000 psi. A die outside themiddle portion and the pressurized water force the middle portion into agenerally triangular cross section while the end portions retain theiroriginal, oval cross-sectional shape. The hydroformed driver side crosstube still has continuous internal and external surfaces.

The generally triangular middle portion has a larger radius of gyrationthan the end portions. Accordingly, the driver side cross tube hasexcellent resistance to twisting, even after a steering column isattached. The triangular middle portion also has greater resistance tovibration than the end portions.

The center stack support is preferably a magnesium alloy casting havinga complex shape that includes several walls having an average thicknessof about 2.5 mm. The center stack support includes a first sleevedefining a first opening for the first wall on the passenger side crosstube, and a second sleeve defining a second opening for the second wallon the drivel side cross tube. Each sleeve includes several ridgesextending radially inwardly of the sleeve wall. The sleeve walls, ridgesand tube walls, in combination, define spaces for a polymeric adhesivebinding the cross tubes to the center stack support.

The crush tubes are preferably cold drawn from an AA 6000 alloy, morepreferably an AA 6061 T4 alloy. The crush tubes have an outer diameterof about 30 mm and a wall thickness of less than about 1.0 mm and about0.7 mm in a particularly preferred embodiment. The crush tubes areinserted into openings in the cross tubes and then welded around theopenings. The crush tubes preferably include one or morecircumferentially extending buckle initiators that are preferablymechanically formed indentations extending around the entirecircumference. The buckle initiators facilitate folding of the crushtubes in an accordion-like manner when impact occurs with an occupant'sknees.

Two crush tubes connect the driver side knee bolster to the driver sidecross tube. The knee bolster is preferably made from aluminum alloysheets. A particularly preferred knee bolster includes a generallyplanar first metal sheet and a second metal sheet defining severalcup-shaped indentations. The indentations have generally flat portionsadjacent the first metal sheet. Additional details of construction of aparticularly preferred knee bolster are shown in Seksaria et al. U.S.Pat. No. 5,244,745 issued Sep. 14, 1993 and entitled “Structural Sheetand Panel”, the disclosure of which is incorporated by reference to theextent consistent with the present invention.

Two other crush tubes connect the passenger side cross tube with theglove box door frame. A glove box door hinged to the frame acts as aknee bolster on the passenger side.

End portions of the passenger side and driver side cross tubes areattached to front hinge pillars through metal end brackets or bracketmeans. The end brackets are preferably stamped from aluminum alloy sheetmaterial having a thickness of about 4 mm. The end brackets are weldedto the cross tubes and then attached to the hinge pillars by metalfasteners extending through openings in both the brackets and in thehinge pillars.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of a motor vehicle body of ourinvention.

FIG. 2 is a perspective view of an instrument panel reinforcementstructure of the present invention.

FIG. 3 is a perspective view of a metal center stack support.

FIG. 4 is a perspective view of a passenger side cross tube.

FIG. 5 is a perspective view of a driver side cross tube.

FIG. 5A is a cross-sectional view taken along the lines 5A—5A of FIG. 5.

FIG. 6 is a perspective view of a metal crush tube.

FIG. 7 is a perspective view of a steering column support beam.

FIG. 8 is a perspective view of a driver side hinge pillar bracket.

FIG. 9 is a perspective view of a passenger side hinge pillar bracket.

FIG. 10 is a perspective view of a driver side knee bolster.

FIG. 10A is a cross-sectional view taken along the lines 10A—10A of FIG.10.

FIG. 11 is a perspective view of a passenger side glove box door.

FIG. 12 is a perspective view of a passenger side airbag housingsupport.

FIG. 13 is a perspective view of a glovebox door frame.

FIG. 14 is a perspective view of a lower support tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The instrument panel reinforcement structure of our invention comprisesa secondary structure attached to a motor vehicle body 20, as shown inFIG. 1. The vehicle body 20 includes a floor or floor panel 22, rightand left front pillars 23, 24, right and left middle pillars 25, 26 andright and left rear pillars 27, 28. The pillars 23, 24, 25, 26, 27, 28extend upwardly from the floor 22, supporting a roof 30. Thereinforcement structure extends between the two front pillars 23, 24 andsupports a steering column, a glove box, a passenger side air bag andvarious other instrument panel components. Some of the instrument panelcomponents may be covered with plastic, wood or leather fascia (notshown).

Referring now to FIG. 2, there is shown an instrument panelreinforcement structure 18. The structure 18 includes a center stacksupport 35 connected on lateral sides with a passenger side cross tube37 and a driver side cross tube 39. The center stack support 35 is amagnesium alloy casting. The passenger side cross tube 37 and the driverside tube 39 are hollow, aluminum alloy extrusions. The passenger sidecross tube 37 has a laterally extending first wall 41 and the driverside cross tube 39 has a laterally extending second wall 43.

The passenger side cross tube 37 has a right end portion 46 connected toa right hinge pillar bracket 47. The driver side cross tube 39 has aleft end portion 48 connected to a left hinge pillar bracket 49. Thebrackets 47, 49 each define through openings 51, 53 for bolts (notshown) or other through fasteners connecting the brackets 47, 49 to thefront pillars 23, 24. As shown in FIGS. 2 and 3, the center stacksupport 35 includes a pair of bottom flanges 54, 55 each definingthrough openings 56 for bolts (not shown) or other through fasteners forconnecting the support 35 to the floor 22.

The center stack support 35 is an AM60B magnesium alloy casting in theparticularly preferred embodiment described herein. The support 35includes a front wall 58 extending between right and left oval sleeves60, 61. The front wall 58 is joined to a shelf 62 and right and leftside walls 64, 65 connected with the flanges 54, 55. The front wall 58,shelf 62 and side walls 64, 65 define a rearwardly opening uppercompartment 67 for a radio and cassette deck (not shown) or otherentertainment/information system. A lower compartment 68 below the shelf62 accommodates the heating/ventilation/air conditioning unit. The frontwall 58, shelf 62, sleeves 60, 61 and side walls 64, 65 have an averagewall thickness of approximately 2.5 mm (0.1 inch).

Referring now to FIGS. 2 and 4, the passenger side cross tube 37 is agenerally cylindrical aluminum alloy extrusion having a laterallyextending first wall 41. The cross tube 37 is made from an AA6063 T4aluminum alloy. The cross tube 37 has an outer diameter of about 60 mm(2.4 inches) and the first wall 41 has a thickness of about 2.8 mm (0.11inch). The cross tube 37 has a right end portion 46 welded to the righthinge pillar bracket 47 and a left end portion 69 nested in a firstsleeve 60 on the center stack support 35. As shown in FIG. 3, the sleevewalls 60, 61 each include several radially inwardly extending ridges 70.The ridges 70 abut against walls 41, 43 of the tubes 37, 39. Connectionsbetween the sleeve walls 60, 61 and the tube walls 41, 43 are alsostabilized by through fasteners (not shown). For example, a bolt orother through fastener extends through an opening 63 in the center stacksupport sleeve 61 and through the wall 43 of the driver side cross tubeend portion 84. The sleeve walls 60, 61 combine with the ridges 70 andtube walls 41, 43 to form several pockets 72 for an epoxy adhesive. Oneimportant advantage of our invention is that the adhesive in pockets 72dampens vibrations transmitted through the center stack support 35 tothe driver side cross tube 39. Accordingly, vibrations transmitted bythe reinforcement structure 18 to the steering column assembly havereduced intensity compared with an instrument panel reinforcementstructure including only a single tube extending between the frontpillars 23, 24.

As shown in FIG. 4, the passenger side cross tube 37 defines two pairsof aligned holes 74, 75. Each pair of holes 74, 75 accommodates a crushtube 78 attached to a glove box door frame 80, as shown in FIG. 2.

As shown in FIGS. 2 and 5, the driver side cross tube 39 is a laterallyextending aluminum alloy extrusion including a second wall 43 having athickness of about 5 mm (0.2 in). The cross tube 39 is made from anAA6063 T4 aluminum alloy. The cross tube 39 has end portions 82, 84 thatare generally oval in transverse section with outer dimensions of about120 mm×60 mm. The left end portion 82 is welded to the left hinge pillarbracket 49 and the right end portion 84 is attached to a sleeve 61 inthe center support 35.

The cross tube 39 is formed with two laterally spaced holes 86, 87 forcrush tubes 78 supporting the driver side knee bolster 90. As shown inFIG. 5A, the cross tube 39 is hydroformed so that a middle portion 83between the end portions 82, 84 has a generally flat bottom surface 92.Two steering column assembly support tubes 94, 95 are secured to thebottom surface 92 by a combination of metal bolts and adhesive bonding.

One important advantage of our invention is that the cross tubes 37, 39are manufactured from hollow, generally cylindrical aluminum alloyextrusions. These closed aluminum alloy shapes provide excellentstiffness in a small volume, with less weight than steel. In addition,spanning the car width with two separate cross tubes rather than onlyone concentrates greater strength and stiffness in the driver side crosstube 39, with greater wall thickness than the passenger side cross tube37.

As used herein, the term “average thickness” refers to the thickness ofa wall in a metal extrusion, averaged around its entire periphery andacross its entire length. The first wall 41 in the passenger side crosstube 37 has an average thickness, t₁, and the second wall 43 in thedriver side cross tube 39 has an average thickness, t₂. The secondwall's average thickness, t₂, is preferably at least 25% greater thant₁, more preferably at least 50% greater, and optimally at least 60%greater. In one preferred embodiment, the first wall 41 has an averagethickness of about 3.0 mm and the second wall 43 has an averagethickness of about 5.0 mm, so that t₂ is approximately 67% greater thant₁.

The hydroformed driver side cross tube 39 has a generally triangularcross-section in the middle portion 83 and a generally oval shape in theend portions 82, 84. The middle portion 83 has a larger radius ofgyration than the end portions 82, 84. Accordingly, the cross tube 39resists twisting more effectively after a steering column is attached.

One of the metal crush tubes 78 is shown in FIG. 6. The crush tube 78has a generally cylindrical wall 98 having an outer diameter of about 30mm and a thickness of about 0.7 mm. A front end portion 99 is attachedto one of the cross tubes 37, 39 and a rear end portion 100 is attachedto the glove box door frame 80 or the knee bolster 90. A portion of thewall 98 is crimped to form an area 105 of reduced diameter that acts asa buckle initiator in frontal collisions.

One of the steering column assembly support tubes 94 is shown in FIG. 7.The support tube 94 has a top wall 110 and a bottom wall 111interconnected by side walls 112, 113. The top wall 110 defines twoapertures 115 a, 115 b aligned with apertures 116 in the bottom wall111, for two metal bolts or other through fasteners (not shown)connecting the bracket 94 to the driver side cross tube 39. In addition,the support tubes 94 are bonded to the cross tube 39 by an adhesivelayer (not shown) between the bottom wall 92 of the cross tube 39 andthe top wall 110 of the support tubes 94.

The top wall 110 also defines two other openings 115 c, 115 d alignedwith openings (not shown) in the bottom wall 111, for connecting thesupport tube 94 to a steering column assembly. The support tube 94 is a6063 T4 aluminum alloy extrusion having a wall thickness of about 5 mm(0.2 in). We avoid welding the steering column support tubes 94 to thedriver side cross tube 39 in order to avoid weakening the metal in bothcomponents.

The left hinge pillar bracket 49 is shown in greater detail in FIG. 8.Two principal panels 120, 121 define axially aligned oval openings 122,123 for the left end portion of the driver side tube. A web 125extending laterally outwardly from the left principal panel 121 definesthree openings 53 for bolts (not shown) fastening the bracket 49 to theleft hinge pillar.

The right hinge pillar bracket 47 is shown in greater detail in FIG. 9.Two principal panels 130, 131 define axially aligned round openings 132,133 for the right end portion 46 of the passenger side tube 37. Alaterally directed web 135 extending from the right panel 130 definesthree openings 51 for bolts (not shown) or other through fasteners,connecting the bracket 47 to the right hinge pillar.

The hinge pillar brackets 47, 49 are stamped from sheets of an AA 6000series aluminum alloy and then formed into the shapes shown in FIGS. 8and 9. Their thickness is about 4 mm (0.16 in).

The driver side knee bolster 90 is shown in greater detail in FIGS. 10and 10A. The knee bolster 90 includes a generally rectangular firstsheet 136 joined with a generally rectangular second sheet 139. Thefirst sheet 136 has an upper edge 137 formed with a downwardly recessedportion 138 to accommodate the steering column. The sheet 136 includes agenerally planar principal portion 140 formed with four generallycup-shaped spaced elements 145 each having a generally flat top portion146 and sidewall portions 147 formed by a sigmoidal line of revolution.The sidewall portions 147 blend smoothly with the top portions 146 andprincipal portion 140, thereby avoiding stress concentrations in theelements 145. The sheet 136 also includes two laterally spaceddepressions 149 extending rearwardly of the principal portion 140. Thedepressions 149 contact rear end portions of the crush tubes.

The glove box door 150 is shown in FIG. 11. The door 150 is a generallyrectangular sheet 151 including a generally planar principal portion 153formed with four generally cup-shaped elements 155. The elements 155each have a generally flat top portion 156 and sidewall portions 157formed by a sigmoidal line of revolution. The sidewall portions 157blend smoothly with the top portions 156 and principal portion 153,thereby avoiding stress concentrations in the elements 155. The glovebox door 150 is attached to a frame 80, as shown in FIG. 2.

The glove box door frame 80 is shown in greater detail in FIG. 13. Theframe 80 includes a laterally extending upper portion 160 and two legs161, 162 extending downwardly from lateral ends of the upper portion160. The legs 161, 162 are formed with rearwardly extending depressions163 164. The depressions 163, 164 are welded to rear end portions of thecrush tubes 78 as shown in FIG. 2.

As shown in FIG. 2, the passenger side cross tube 37 carries a supportplatform 170 for the air bag housing. Referring flow to FIG. 12, theplatform 170 includes a generally planar main panel 171 and a recessedportion 172 offset forwardly from the main panel 171.

As shown in FIG. 2, a passenger side support lower support tube 180extends between the passenger side hinge pillar bracket 47 and thecenter stack support 35. The glove box frame 80 is attached to alaterally extending base 182. The lower support tube 180, shown ingreater detail in FIG. 14, is an extruded hollow tube bent at an elbow186 between a laterally extending base 182 and an upwardly extending arm184. The lower support tube 180 is an aluminum alloy extrusion.

Referring again to FIG. 2, a driver side support tube 180 extendsbetween the left hinge pillar bracket 49 and the center stack support35. The driver side knee bolster 90 is fixed to a laterally extendingbase 182 of the support tube 180. The support tube 180 is an aluminumalloy extrusion, as shown in greater detail in FIG. 14.

The knee bolster 90, glove box door 150 and glove box door frame 80 areeach made from sheets of an AA 5000 series aluminum alloy having athickness of about 1.5 mm (0.06 in). The knee bolster 90 and glove boxdoor 150 are made in accordance with Seksaria et al U.S. Pat. No.5,244,745 issued Sep. 14, 1993, the disclosure of which is incorporatedby reference.

Having described the presently preferred embodiments, it is to beunderstood that the invention may be otherwise embodied within the scopeof the appended claims.

What is claimed is:
 1. An instrument panel reinforcement structure foruse in a vehicle body having a floor panel and a plurality of pillarsextending outwardly from said floor panel, said reinforcement structurecomprising: (a) a passenger side cross tube comprising a hollow metalextrusion having a laterally extending first wall; (b) a driver sidecross tube spaced laterally from said passenger side cross tube andcomprising a single hollow metal extrusion having a laterally extendingsecond wall thicker than said first wall, said driver side cross tubecomprising opposed end portions, at least one of said end portionshaving a generally oval cross section; and (c) a center stack supportbetween the passenger side and driver side cross tubes, said centerstack support defining openings for connection with end portion of saidcross tubes.
 2. The reinforcement structure of claim 1 wherein saidfirst wall has an average thickness t₁, said second wall has an averagethickness t₂, and t₂ is at least 25% greater than t₁.
 3. Thereinforcement structure of claim 1 wherein said first wall has anaverage thickness t₁, said second wall has an average thickness t₂, andt₂ is at least 50% greater than t₁.
 4. The reinforcement structure ofclaim 1 wherein said first wall has an average thickness t₁, said secondwall has an average thickness t₂, and t₂ is at least 60% greater thant₁.
 5. The reinforcement structure of claim 1 wherein said passengerside cross tube has a first length extending laterally outwardly of saidcenter stack support and the first wall has a thickness t₁ that isgenerally constant across said first length.
 6. The reinforcementstructure of claim 1 wherein said driver side cross tube has a secondlength extending laterally outwardly of said center stack support andsaid second wall has a thickness t₂ that is generally constant acrosssaid second length.
 7. The reinforcement structure of claim 1 whereinsaid passenger side cross tube is generally cylindrical and said driverside cross tube comprises said opposed end portions each having agenerally oval cross section.
 8. The reinforcement structure of claim 7wherein said first wall has an average thickness t₁, said second wallhas an average thickness t₂, and t₂ is at least 25% greater than t₁. 9.The reinforcement structure of claim 1 wherein said passenger side anddriver side cross tubes each comprise a unitary aluminum alloyextrusion.
 10. The reinforcement structure of claim 1 furthercomprising: (d) at least one steering column assembly support tubeattached to said driver side cross tube.
 11. The reinforcement structureof claim 10 wherein said support tube is formed with apertures forbolting said driver side cross tube.
 12. The reinforcement structure ofclaim 1 wherein said first wall and said second wall each comprise analuminum alloy of the AA 5000 or 6000 series.
 13. A vehicle bodycomprising a floor panel, first and second front pillars extending fromsaid floor panel, and an instrument panel reinforcement structureextending between said front pillars, said instrument panelreinforcement structure comprising: (a) a passenger side cross tubecomprising a hollow metal extrusion having a laterally extending firstwall; (b) a driver side cross tube spaced laterally from said passengerside cross tube and comprising a single hollow metal extrusion having alaterally extending second wall thicker than said first wall, saiddriver side cross tube comprising opposed end portions, at least one ofsaid end portions having a generally oval cross section; and (c) acenter stack support between the passenger side and driver side crosstubes, said center stack support defining openings for connection withend portions of said cross tubes.
 14. The vehicle body of claim 13further comprising a metal first bracket connecting an end portion ofsaid first wall to a front pillar and a metal second bracket connectingan end portion of said second wall to a front pillar.
 15. An instrumentpanel reinforcement structure for a vehicle body, said reinforcementstructure comprising: (a) a passenger side cross tube comprising ahollow metal extrusion extending in a cross-car direction; and (b) adriver side cross tube spaced from said passenger side cross tube andextending in a cross-car direction, said driver side cross tubecomprising a hollow metal extrusion having two end portions and a middleportion between said end portions, at least one of said end portionshaving a generally oval cross-sectional shape, said middle portionhaving a cross-sectional shape different from said end portions.
 16. Thereinforcement structure of claim 15 wherein said middle portion has alarger radius of gyration than said end portions.
 17. The reinforcementstructure of claim 15 wherein said middle portion has greater resistanceto vibration than said end portions.
 18. The reinforcement structure ofclaim 15 wherein each said cross tube comprises an aluminum alloy of theAA 5000 or 6000 series.